1. Field of the Invention
The present invention relates to a technique of feeding coating liquid to various substrates such as a semiconductor wafer, a glass substrate for liquid crystal display or a reticle substrate for photomask, to form a liquid film of the coating liquid on the surface of such a substrate.
2. Description of the Background Art
Conventionally, the coating process of resist liquid performed to obtain a desired circuit pattern in manufacturing of a semiconductor device or the like has been carried out by a so-called spin coating method. This method is to form a liquid film (resist film) on the entire surface of a wafer by feeding coating liquid from a nozzle provided above a middle portion of the wafer, which is a substrate to be processed, horizontally held by a rotatable spin chuck or the like, while rotating the wafer for diffusion of the resist liquid by the centrifugal force of the wafer.
To accommodate the recently-increasing demand of miniaturization of circuit patterns, it is required to reduce the thickness of the resist film. In the spin coating method, the number of rotations of the wafer has been increased to meet such a requirement. If the wafer is rotated at a high speed, however, turbulent flow is likely to occur on the wafer surface especially when the wafer has a large size. The turbulent flow would cause unevenness of the film thickness on the entire wafer, which would make difficult to reduce the size of a pattern. Accordingly, the inventors have studied application of a coating film forming apparatus not using the spin coating method.
FIG. 23 shows an example of a nozzle unit in which a nozzle and a driving mechanism for moving the nozzle in the X-direction (from side to side) are integrated. A case body 11 shown in FIG. 23 is constituted by a front portion 12 and a rear portion 13. The upper and lower surfaces of front portion 12 are each provided with a slit 14 (not shown for the lower surface side), which defines the direction of movement of a coating liquid feed tube 15 provided through slit 14. A nozzle portion 16 for discharging the coating liquid downward is arranged at a tip of coating liquid feed tube 15. Coating liquid feed tube 15 and nozzle portion 16 are configured to move back and forth within an area defined by slit 14, by actuation of a belt driving portion 17 provided in rear portion 13.
At the coating process, nozzle portion 16 is moved back and forth (a scan is performed) in the X-direction as described above, while a wafer W placed below nozzle portion 16 is intermittently fed in the Y-direction. Further, the width of movement in the X-direction is changed in accordance with the width of a region to be fed with coating liquid, every time the intermittent feeding in the Y-direction is performed, to allow the coating liquid to be fed onto the surface of wafer W in the manner of a so-called single stroke of the blush.
However, as the method above is to form a liquid film on the entire wafer surface by lining up linear coated regions side by side, scanning time per one row of nozzle portion 16 must be shortened in order to reduce the total time required. For the time reduction, it is effective to move nozzle portion 16 at a high speed. Such operation, however, causes large vibration at e.g. belt driving portion 17, which is propagated to pulsate the coating liquid in coating liquid feed tube 15, causing variation in the pressure within coating liquid feed tube 15. The change in the pressure in coating liquid feed tube 15 is directly reflected in the discharge pressure of the coating liquid at nozzle portion 16, resulting in non-uniform feeding of the coating liquid from discharge opening 16a of nozzle portion 16, as shown in FIG. 26.
The present invention was made to solve the problems described above, and an object of the invention is to provide a technique that allows, in forming of a coating film on the surface of a substrate by feeding coating liquid onto the substrate while moving a nozzle portion from side to side, stabilization of discharge of the coating liquid and formation of a coating film having high in-plane uniformity in the film thickness.
In order to solve the problems above, various approaches have been presented such as provision of a shock-absorbing movable body (balancer) at belt driving portion 17, which moves in a direction opposite and symmetrical to the movement of nozzle portion 16, or application of high pressure air to the periphery of a guide member (not shown) of nozzle portion 16 for suppressing mechanical friction at moving of nozzle portion 16. It was, however, difficult to completely remove vibration itself propagated to nozzle portion 16, and thus variation in the discharge pressure could not be sufficiently reduced by such approaches. The present inventors, therefore, have continuously pursued the reasons therefor, and have made an attempt to form a line of coating liquid on the surface of the wafer while moving nozzle portion 16 at 1 m/sec in the apparatus described above, and measure the surface height of the line with respect to time at the section of interest, to find that the surface has regular concave and convex portions at frequency of e.g. 200 Hz. This is assumed to be one cause of the vibration, since the frequency corresponds to the cycle at which groove 18a on the surface of belt 18 is engaged with tooth 19a on the surface of a cam 19 in belt driving portion 17 shown in FIGS. 27A and 27B. As illustrated, grooves 18a and teeth 19a are both formed in parallel, and it is assumed that the vibration occurs when the tip of tooth 19a touches the inner surface of groove 18a, which is repeated.
According to one aspect of the present invention, a coating film forming apparatus includes a substrate holding portion holding a substrate, a nozzle portion feeding coating liquid to the substrate held by the substrate holding portion via a discharge opening formed at a tip, a coating liquid feed path feeding coating liquid to the nozzle portion, a channel connecting the discharge opening and the coating liquid feed path in the nozzle portion and having a section larger in a diameter than the discharge opening, a pressure loss portion causing pressure loss in the coating liquid flowing through the channel, a first driving portion moving said nozzle portion in a first direction (side-to-side direction) along a substrate surface, and a second driving portion intermittently moving said nozzle portion relative to the substrate in a second direction (back-and-forth direction) crossing said first direction. The nozzle portion is moved in the side-to-side direction to apply the coating liquid linearly on the substrate surface, and is intermittently moved relative to the substrate such that the linear coated regions are lined up in the back-and-forth direction.
In such a structure, even if pulsation occurs in the coating liquid feed path due to vibration caused at the first driving portion at moving of the nozzle portion in the side-to-side direction, the pressure loss portion in the nozzle portion can absorb the pulsation, preventing propagation of the vibration to the discharge opening side. Accordingly, the discharge pressure of the coating liquid at the discharge opening is stabilized, so that a coating film having a high in-plane uniformity in the film thickness can be formed on the substrate surface. For the pressure loss portion, preferably, a filtering member is used, and specifically, a tubular body formed by layering a plurality of porous bodies, having one end opened may be used. In addition to the effects described above, such a structure allows removal of impurities from the coating liquid as the coating liquid passes through the filtering member, so that a coating film having high purity can be formed on the substrate, improving a product yield.
Moreover, the nozzle portion may be a sphere provided with a channel having a portion with a circular cross section, the circular portion being closed by the pressure loss portion, the sphere having microscopic concave portions formed on the surface thereof such that a small gap is produced between the sphere and the circular portion. The nozzle portion may also be configured to have a channel provided with a first liquid pool portion larger in diameter than the discharge opening, a communicating channel smaller in diameter than the first liquid pool portion, and a second liquid pool portion larger in diameter than the communicating channel, in this order from the discharge opening side. Either structure can absorb the pulsation occurring at the coating liquid feed path side, and can prevent propagation thereof to the discharge opening side. It is noted that the filtering member and the sphere may more effectively be arranged within a liquid pool portion formed in a channel, having a diameter larger than either one of the diameters at the upper end of the discharge opening and at the tip end of the coating liquid feed path.
Preferably, the coating film forming apparatus further includes a coating liquid feed portion applying a pressure on coating liquid to feed the coating liquid to the nozzle portion, and a flowmeter measuring a flow rate of coating liquid in a channel from the coating liquid feed portion to the nozzle portion. The flow rate from the coating liquid feed portion to the nozzle portion is adjusted in accordance with the flow rate of the coating liquid measured by the flowmeter.
According to another aspect of the present invention, a coating film forming apparatus includes a substrate holding portion holding a substrate, a nozzle portion feeding coating liquid to the substrate held by the substrate holding portion, a first driving portion moving the nozzle portion in a first direction (side-to-side direction) along a substrate surface, a vibration absorbing means interposed between the first driving portion and the nozzle portion so as to suppress propagation of vibration occurring at the first driving portion to the nozzle portion, and a second driving portion intermittently moving the nozzle portion in a second direction (back-and-forth direction) crossing the first direction relative to the substrate. The nozzle portion is moved in the side-to-side direction to apply the coating liquid linearly on the substrate surface, and is intermittently moved relative to the substrate such that the linear coated regions are lined up in the back-and-forth direction.
Such a structure allows the vibration absorbing means to absorb the vibration occurring at the first driving portion, preventing propagation of the vibration to the nozzle portion side. Preferably, the vibration absorbing means includes a portion made of an elastic body between the first driving portion and the nozzle portion, the elastic body being, for example, rubber, leaf spring or the like.
Preferably, the coating film forming apparatus further includes a coating liquid feeding portion applying a pressure on coating liquid so as to feed the coating liquid to a nozzle portion, and a flowmeter measuring a flowrate of the coating liquid in the channel from the coating liquid feed portion to the nozzle portion. The flowrate from the coating liquid feed portion to the nozzle portion is adjusted in accordance with the flowrate of the coating liquid measured by the flowmeter.
According to a further aspect of the present invention, a coating film forming apparatus includes a substrate holding portion holding a substrate, a nozzle portion feeding coating liquid to the substrate held by the substrate holding portion, a first driving portion moving the nozzle portion in a first direction (side-to-side direction) along a substrate surface, and a second driving portion intermittently moving the nozzle portion relative to the substrate in a second direction (back-and-forth direction) crossing the first direction. The first driving portion includes an endless belt provided along the side-to-side direction so as to correspond to a movement region of the nozzle portion, and having an inner surface on which a number of grooves and teeth are formed extending in parallel so as to form an acute angle to the first direction, and a pair of pulleys having grooves and teeth engaged with the grooves and teeth of the endless belt over an entire side circumferential surface such that the endless belt can be rotated. The nozzle portion is moved in the side-to-side direction to apply the coating liquid linearly on the substrate surface, and is intermittently moved relative to the substrate such that the linear coated regions are lined up in the back-and-forth direction. Such a structure can prevent occurrence of vibration itself at a vibration source, allowing stabilized discharge pressure of the coating liquid from the nozzle portion.
Preferably, the coating film forming apparatus further includes a coating liquid feed portion applying a pressure on coating liquid to feed the coating liquid to the nozzle portion, and a flowmeter measuring a flow rate of coating liquid in a channel from the coating liquid feed portion to the nozzle portion. The flow rate from the coating liquid feed portion to the nozzle portion is adjusted in accordance with the flow rate of the coating liquid measured by the flowmeter.
The present invention also includes the structure below. The coating film forming apparatus includes a substrate holding portion holding a substrate, a nozzle portion feeding coating liquid to the substrate held by the substrate holding portion via a discharge opening formed at a tip, a coating liquid feed path feeding coating liquid to the nozzle portion, a first driving portion moving the nozzle portion in a side-to-side direction, and a second driving portion intermittently moving the nozzle portion relative to the substrate in a back-and-forth direction.
By moving the nozzle portion in the side-to-side direction, the coating liquid is linearly applied onto the substrate surface, the nozzle portion being intermittently moved relative to the substrate such that the linear coated regions are lined up in the back-and-forth direction. The coating film forming apparatus further includes at least two of the components (A) to (C) as follows:
(A) a pressure loss portion that connects the discharge opening with the coating liquid feed path in the nozzle portion, and causes pressure loss at a channel having a section larger in diameter than the discharge opening and at the coating liquid flowing through the channel,
(B) a vibration absorbing means interposed between the first driving portion and the nozzle portion so as to prevent propagation of vibration occurring at the first driving portion to the nozzle portion, and
(C) the first driving portion being provided along the first direction to correspond to the movement region of the nozzle portion, an endless belt having an inner surface on which a number of grooves and teeth are formed extending in parallel so as to form an acute angle to the first direction, and a pair of pulleys formed over the entire side circumferential surface of a groove and a tooth engaged with the groove and the tooth so as to rotate the endless belt.
Such a structure can further improve stabilization of the discharge pressure of the coating liquid at a discharge opening, which is a common object of the components above.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.